Mixtures based on oxazolidines and organic polyisocyanates capable of being hardened by water have already been disclosed, for example, in German Offenlegungsschrift No. 2,018,233 (U.S. Patent Specification No. 3,743,626). In German Offenlegungsschrift No. 2,446,438, it is also mentioned that the isocyanate-free oxazolidines described there constitute reactants for organic polyisocyanates which become active only in the presence of moisture and after hydrolytic ring opening.
The mixtures described in German Offenlegungsschrift No. 2,018,233 have, however, various disadvantageous properties. The storage life of systems which are highly reactive due to the presence of aromatic polyisocyanates is very brief even if moisture is excluded. On the other hand, stable preparations based on aliphatic polyisocyanates harden too slowly when exposed to moisture. In particular, it should be noted that, in solvent-free systems used for thick coatings, the skin develops too slowly and when finally formed is too dense and therefore prevents any further penetration of moisture into the coating composition so that complete drying proceeds too slowly. As a result, these coatings often attain their ultimate strength only after weeks or even months and are therefore not suitable for all commercial applications. The surface characteristics of coatings obtained from the preparations according to German Offenlegungsschrift No. 2,018,233 also fail to meet the practical requirements in particular in the case of solvent-free systems and when isocyanate prepolymers are used as the polyisocyanate component. The surface of such coatings is blocking and slightly tacky so that particles of dust and dirt collect on the surface.
It was therefore an object of the present invention to provide new systems which would be free from these disadvantages.